What Schrödinger's Cat Really Tells Us About Reality

0:00 catch us up on entangled particles. Well, this is part of this fact that we said before that there's not a separate quantum wave function for every individual thing in the universe. There's only one wave function for all of them at once. And what the wave function tells us is the probability of observing something. So if you have two particles and let's say they have positions, you don't know where it is. In fact, literally when something like the Higs Bzon decays, decays into an electron and a positron, the anti-electron, and you say, "Well, what direction are they going in?" And the answer is they're both going in all directions. Their wave functions are coming out sort of in a spherical pattern. But then when you observe one of them, that's where it is. That's where it is. And and momentum is conserved. So now you know the other one is going exactly. So you know where the

0:46 other one is without having detected it yet. That's entanglement. So, what entangles them? The rules of physics. Okay, that doesn't that's not Stop it. That doesn't do that. Get out of here. That's my mother saying because I said so. That's what that mom, why can't I have ice cream for breakfast? Because I said so. That's why. What law of physics prescribes this? Quantum mechanics. That's the nature of quantum mechanics. It's sort of that this is how science works. If you sort of conjecture an idea, then you say, is that right or not? And so in quantum mechanics, the the fundamental way things work is that the state of the universe is a vector in Hilbert space, which means that the combined state of every particle in the

1:33 universe and every field and every everything is described by one single mathematical object. And in fact, I don't like the word entanglement because it kind of it makes it hard to update your intuition. And it makes it sound like what really exists are these two particles and you measure one and you're like why did the other one change? If you just accept that what exists is the combined quantum state of everything in the universe then it's no surprise at all that when you look at a little bit of it affects the rest. Okay. But interesting. Can I just take two random particles that were not born together and entangle them? Sure. Okay. Yeah. Entanglement happens whenever you have two objects that are not entangled, but they interact with each other in different ways depending on different

2:19 parts of their wave function. So, let me just give you a downto-earth example. Schrodinger's cat, right? You've heard about this. Schroinger, uh, who apparently didn't like cats, uh, goes to a great amount of thought experiment effort to put a cat in a superp position. That's right. That would have never worked with Schroinger's dog. That would that would not have people wouldn't have had it. said that he didn't like cats. This is why he picked the cat. So, it's in a superp position of alive and dead. I'm a cat person. So, I in my version they're super position of awake and asleep. A it's very sweet. You don't have to kill the cat. You don't have to kill it. I didn't know you didn't have to kill. The point is you don't have to kill the cat. But the point is they're different places in the box. Okay. And what that means is that everything in the box, the air, the light, you know, everything

3:05 moving around in the background interacts differently with the awake cat running around trying to get out and the asleep cat just snoring peacefully on the ground. And so the environment, as we say, entangles with the cat right away because it interacts with it, but interacts with it differently depending on different parts of the wave function. Okay. I don't know that that's more clear to me. So you're you're sleep and awake cat. But we declared that without actually sticking asleep and awake cat in the box. I mean we just asserting that. Why does that make it let the cat just be drowsy in between? You know this is in and out. This is Schroinger's whole point. This is why he set up in the in the experiment. There's a radioactive

3:51 substance thought experiment. He didn't do it. So radioactivity and there's a geer counter and the geer counter will click when it detects a radioactive decay. In radioactivity you have no idea which particle is going to decay. Okay, just statistically you know very accurately what fraction of them will. But the fact that you don't know creates a brilliant beautiful random number in a sense. Yeah. Okay. So if you needed a random thing, you get a decaying set of particles and you can build you can draw randomness from that that is as that's as good a random as we can 100% random as far as we know right nothing nothing better and this is you know the 1930s when shinger was very unhappy with the state of quantum mechanics he was not bragging about quantum mechanics he was

4:37 saying surely you don't believe this and he says when we say this particle has a probability of decaying what quantum mechanic actually says is there's a wave function for the particle and it is in a superp position of I have decayed and I have not decayed. Uhhuh. And the part of it that is decayed sets off the geer counter. So now the geer counter is in a superp position of I have clicked and I have not clicked. And the geer counter in the part that clicks knocks over a hammer, breaks a vial full of sleeping gas and the cat goes to sleep. So the cat goes into a superp position of being awake and being asleep. That's the whole point of the sort of Rube girl Rub Goldberg gizmo that Sherninger builds in

5:23 there. But how does that help anything? Like well Sherninger is trying to say in in the way that we thought of quantum mechanics back then there was these giant debates between Boore and Einstein about what quantum mechanics really means. Neils Boore and Neils Boore would have said, "Look, when you open the box and look, the cat suddenly changes from being in a superp position of awaken asleep to being one or the other." Okay. And Schroinger is like, "Come on." You think that when I look at it, it changes like that? I got you. I got you. So, his thing is that superp position exists at all times, everywhere, no matter what. And it has nothing to do with the fact that I looked at it. It's in that superp position. You just got to accept that. He should have said that. He he blinked.

6:09 He lost courage at the last second. And it was uh a decade and a half later uh or two decades later, a graduate student at Princeton named Hugh Everett said exactly those words. He said, "Just believe what the what the formula is telling you." And what the formula tells you is when you look at it, guess what? You enter into a superp position. There's a part of you that has seen the cat awake and a part of you that has seen the cat asleep. And Hugh Everett says that's because both of those possibilities exist just in two separate worlds. Because what we're dealing with is a probability in the first place. So that always exists. It doesn't change because you observed it. It's still the same. You just mentioned in that world I have some memory that I haven't heard

6:56 about lately, but the Copenhagen interpretation that was Neils Bore. Neils Boore is is Danish. Okay. And so they credited I guess the city but it was really a a boore interpretation not a Copenhagen. Well he had his people who would come into his institute and hang around and go out you know spreading the gospel of bore. So this was the idea. Yeah. Heisenberg powi there's a bunch. There's a bunch. Okay. So uh can you catch us up on the many worlds interpretation? Right. So the Copenhagen interpretation really frustrated people like Einstein and Schroinger because it seemed to give up on arguably the single most crucial feature of science which is realism about the physical world. You know before quantum mechanics came along

7:41 you knew there was a real world out there even if you didn't know exactly what it was doing. And Boore and his friends seem to be saying that before you open the box and look at the cat, there is no fact of the matter about what the cat is. And Einstein Schwinger said, you know, even if you don't know what the fact of the matter is, there should be some. And so Everett sort of lives up to the dreams of Einstein and Schroinger and says, "Yes, there is a reality there, but sadly for you, the reality is there's many different worlds and they don't interact with each other." So Everett is just saying that in this world of superp positions that quantum mechanics always describes, you should just take them all seriously. They're

8:27 all actually there. It's not just a mathematical trick. That is really, really tough. I get it. That is rough. You got the sleepy cat, you got the awake sleep cat, you got the awake cat. Is there a world where I open the box and I see the awake cat as a different world from the one in which I open the box and it's asleep. There is there are well there will be two worlds and it happens long before you open the box because as soon as the other stuff in the box as soon as the photons and the atoms and everything become entangled with the cat boom there's two worlds. So where are those two worlds or is that the wrong question? That's the wrong question. I I see that you quickly got it. As soon as you asked it, you knew. No, I knew. But the worlds are not located in space.

9:13 Space is located in the world. Holy crap. He knows it. Chuck gets it. He gets it. I need you, Chuck. Chuck, I need you for this. I don't believe you today anymore. It's over now. There is no God. Oh, no. I mean, that's also true, but okay. Whole another podcast.